1. Technical Field
The present invention relates generally to a closure assembly for a shipping and storage container, and more particularly toward an improved cover and gasket for sealing a material containing drum.
2. Background Art
Shipping and storage containers which have a cylindrical drum and removable lid are generally well known for reliably storing and/or transporting a variety of materials. In order to fill the drums, the lid is removed to define an opening in one end face of the drum and material is introduced into the drum. After filling is completed, the lid is replaced and appropriately secured to the drum.
In a typical storage drum, a cylindrical sidewall extends upwardly from a transverse base and terminates at an annular chime or bead at the top end of the drum. The chime has a rounded contour. In order to produce a seal between the lid and the drum when the lid is secured to the drum, liquid rubber or other resilient material is poured into a groove in the underside of the lid when the lid is inverted. The liquid is cured to form a solid compliant gasket which is adhered to the underside of the lid and the lid is fastened to the top of the drum.
The problem with using a poured gasket is that due to surface tension and related cohesion forces, the liquid develops a convex outer surface or meniscus which results in a corresponding rounded mating surface on the cured gasket. When the lid is fastened to the drum, the rounded chime engages the oppositely curved surface on the gasket. As a result, only a line contact is achieved between the gasket and the drum around the periphery of the open end. It is also possible for the gasket to "roll off" the top end face of the drum and further compromise the integrity of the seal.
In addition, non-uniformities in the liquid material and the resulting gasket cause localized zones of irregular hardness. When fastening force is applied to the lid, the variations in hardness cause "high spots" and "low spots" in the gasket and limit the effectiveness of the seal. Because the cured gasket is bonded to the lid, when unacceptable variations in the density of the cured liquid occur, the entire lid must be discarded.
The present invention is directed toward overcoming the persistent problems discussed above.